1. Field of the Invention
The present invention relates to a replaceable sealing member and, more particularly, to a unitized or monolithic lip seal with reinforced backup to limit elastomeric flow.
2. Description of the Background
In the past, various types of elastomeric lip seals have been used for general sealing purposes including, for instance, sealing around shafts and for sealing engagement between piston-cylinder mechanisms. Typical uses of elastomeric lip seals may include oil field mud pump applications such as dual- and single-acting mud pump pistons.
The flexible nature of the lip seal allows it to elastically seal with respect to a sealing surface, e.g., between a mud pump piston and a cylinder liner. However, the same flexible nature of the elastomeric lip seal makes it susceptible to extrusion forces that tend to tear, cut, or bite into the flexible lip seal material. Extrusion may occur, for example, if elastomeric material is compressed between the metallic hub portion of a mud pump piston and a metallic cylinder lining so as to be pinched upon relative movement of the two components. The elastomeric material bulges or stretches or flows under pressure into regions where the elastomeric material may be damaged. Elastomeric flow refers to the stretching or bulging of the elastomeric material to a different relative position in response to pressure. When the pressure is removed, the elastomeric material returns to the same general position. Lip seal extrusion deteriorates the condition of the seal at a rate that depends upon various factors such as lip seal flexibility, pump pressures, piston speed, types of slurries pumped and other factors.
One method for alleviating extrusion damage involves the use of a reinforcement section to limit the elastic flow of the flexible elastomeric lip seal material. Such reinforcement sections effectively form a restriction that confines or limits flow of the elastomeric lip seal material to avert extrusion.
In general, to produce a piston having a reinforcement section of this type, the reinforcement section is first machined into the metal hub of the mud pump piston. A body section having a protruding lip seal thereon is then molded or bonded to the metal hub. More specifically, it is necessary to take the following steps: (1) machine the metal hub to form the desired reinforcement section contour; (2) clean and treat the machined metal hub with a bonding agent; (3) insert the metal hub into a mold along with the elastomeric material; and (4) cure the elastomeric material to bond it to the hub typically by heating the hub along with the elastomer.
Because a complete mud pump piston is quite heavy (in many cases well over 50 lbs.), special handling during manufacture is necessary. Furthermore, significant energy is expended in the curing process due to the large mass of the piston hub, which absorbs a significant amount of heat energy.
Consequently, there remains the need for an improved, replaceable sealing member that offers dependable operation at reduced levels of capital investment. Those skilled in the art have long sought and will appreciate the present invention, which substantially alleviates these and other problems.